My wife and I lived apart for all three school years. (No kids, which made it a lot easier, of course.) She had a good job near Philly, and while I seriously considered Penn, in the end we decided it would be worth the sacrifice for me to go to HLS.
It's definitely do-able, at least if you don't have kids. The longest stretch we were apart was 7 weeks(!), right at the start of 1L year. After that, I started flying home roughly every other weekend. During the summers, I worked at a firm near our home. Fortunately, between my wife's job and my summer work, we could afford having the separate (dumpy) apartment and the travel back and forth. (One of my classmates wasn't so lucky -- she used to travel from HLS to Baltimore frequently to see her boyfriend, by Peter Pan bus.)
The toughest thing for me was not the loneliness but the temptation. A few of my non-trad classmates got divorced during LS. I made a promise to myself that my marriage would not become a statistic, and I managed to barely muddle through without doing anything I overly regret.